Lee Love on wed 18 aug 10
On Wed, Aug 18, 2010 at 10:27 PM, John Post wro=
=3D
te:
> Last winter I wanted to make some outdoor garden pieces. =3DA0I used
> Rovin's RO-82, a terra cotta body with grog and single fired it to
> cone 1-2.
John, Continental Clay recommends firing their terracotta to cone
1-2 for outdoor sculpture. Most problems with absorbancy in lowfire
clays are related to under-firing.
My terracotta is single fired to cone 3 with terra sig (no glaze)
rings nicer than porcelain and works great in the oven and microwave.
As Pete Pinnell has reported, it is as strong or stronger than
stoneware.
I have seen the same clay fired to cone 6 with no ill effect. I
am guessing white bodies don't have the same range.
Evidently, Rex is going to paint his sculpture so he probably isn't
concerned with these aspects.
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Rex Greg on wed 18 aug 10
Hi, back in college I did a lot of sculpting with clay. I am looking to =
=3D
get back=3D20
into it, but have a question that I never thought to ask back then.=3D20=3D=
20=3D
So, my sculptures are non-utilitarian, and I generally do not glaze them =
=3D
(I=3D20
usually paint them). I wanted to know, if I were to fire a piece to cone=
=3D
05,=3D20
would a low fire clay whose max firing temp is cone 05 be any stronger/mo=
=3D
re=3D20
durable than a high fire clay (say a cone 10 clay) fired to the same=3D20
temperature (cone 05)? Or would the high fire clay be more durable, or w=
=3D
ould=3D20
they be the same? What about two high fire clays, say cone 6 and cone 10,=
=3D
=3D20
both fired to cone 6? Which if any would be stronger/more durable?
I always used high fire clays (cone 10) in college because that's what=3D20=
=3D
everyone else in the studio used, as many of them were potters who glazed=
=3D
=3D20
their pieces. But my sculptures were usually just bisqued, and rarely fir=
=3D
ed to=3D20
cone 1 or 2. Are low fire clays suitable for somewhat large sculptures (=
=3D
from=3D20
bust to torso sized)?=3D20=3D20
Thanks!
Nancy Udell on wed 18 aug 10
Hi Rex,
Setting aside actual strength, I think the main requirement for
outdoor sculpture is that it be vitrified -- so fired completely to
whatever cone the clay can go to. You don't want something outside
that can take on water. After that, you have to test your vitrified
clay for absorption rate. Page 17 of the Val Cushing Handbook deals
with this. "Testing for percentage of absorption and C/B value --
safe outdoor clay sculpture body for winter climates." He says "a
proper outdoor clay sculpture body will have a C/B ratio of 0.78
(approx)" There is a complicated formula to determine the C and B
values. It relates to weighing the piece dry, soaked for 24 hours,
boiled for three hours and then doing some math.
I will say that if i were thinking of using a low fire body outside, I
might do this. But I have been using a commercial cone 6 stoneware
fired to temp for 5 years for outdoor sculpture and have had zero
breakage rate (due to weather, as opposed to stupidity). We've had A
LOT of snow and winter freezing and thawing here in the last five
years, so I feel pretty good about it.
Good luck
Nancy in Santa Fe
clayandcolor.net
On Aug 18, 2010, at 11:16 AM, Rex Greg wrote:
> Hi, back in college I did a lot of sculpting with clay. I am
> looking to get back
> into it, but have a question that I never thought to ask back then.
>
> So, my sculptures are non-utilitarian, and I generally do not glaze
> them (I
> usually paint them). I wanted to know, if I were to fire a piece to
> cone 05,
> would a low fire clay whose max firing temp is cone 05 be any
> stronger/more
> durable than a high fire clay (say a cone 10 clay) fired to the same
> temperature (cone 05)? Or would the high fire clay be more durable,
> or would
> they be the same? What about two high fire clays, say cone 6 and
> cone 10,
> both fired to cone 6? Which if any would be stronger/more durable?
>
> I always used high fire clays (cone 10) in college because that's what
> everyone else in the studio used, as many of them were potters who
> glazed
> their pieces. But my sculptures were usually just bisqued, and
> rarely fired to
> cone 1 or 2. Are low fire clays suitable for somewhat large
> sculptures (from
> bust to torso sized)?
>
> Thanks!
Guangzhen Zhou on wed 18 aug 10
Hello Rex=3D2C
=3D20
I am a sculptor too.
I will say yes=3D2C if you got your pieces fired in high temperature that w=
il=3D
l be stronger/more durable than low fired temperature.=3D20
But=3D2C if your pieces are small and for in-door only=3D2C that will be OK=
for=3D
low fire. not much different.
The good part is: it will be easier for paint over on low fire clay. You ma=
=3D
y feel like painting on glass what the clay got high fired.
You may take look at my low fired pieces at: www.ChineseclayArt.com or=3D20
http://www.facebook.com/home.php?#!/profile.php?id=3D3D100000114810945&v=3D=
3Dph=3D
otos
=3D20
Good luck on your new pieces!=3D20
Guangzhen "Po" Zhou Chinese Clay Art Corp. / ClayGround Clay Art Supplies a=
=3D
nd Studio 1155 S. De Anza Blvd. San Jose=3D2C CA 95129 Mailling address: PO=
B=3D
ox 1733=3D2C Cupertino=3D2C CA 95015 Tel. 408-343-3919=3D2C Fax. 408-343-01=
17 www=3D
.ChineseClayArt.com=3D2C ChineseClayArt@hotmail.com Art Tools are Part of A=
rt=3D
Works.
=3D20
> Date: Wed=3D2C 18 Aug 2010 13:16:15 -0400
> From: rexgregorius@AOL.COM
> Subject: High Fire vs. Low Fire for sculpting
> To: Clayart@LSV.CERAMICS.ORG
>=3D20
> Hi=3D2C back in college I did a lot of sculpting with clay. I am looking =
to=3D
get back=3D20
> into it=3D2C but have a question that I never thought to ask back then.=
=3D20
>=3D20
> So=3D2C my sculptures are non-utilitarian=3D2C and I generally do not gla=
ze t=3D
hem (I=3D20
> usually paint them). I wanted to know=3D2C if I were to fire a piece to c=
on=3D
e 05=3D2C=3D20
> would a low fire clay whose max firing temp is cone 05 be any stronger/mo=
=3D
re=3D20
> durable than a high fire clay (say a cone 10 clay) fired to the same=3D20
> temperature (cone 05)? Or would the high fire clay be more durable=3D2C o=
r =3D
would=3D20
> they be the same? What about two high fire clays=3D2C say cone 6 and cone=
1=3D
0=3D2C=3D20
> both fired to cone 6? Which if any would be stronger/more durable?
>=3D20
> I always used high fire clays (cone 10) in college because that's what=3D=
20
> everyone else in the studio used=3D2C as many of them were potters who gl=
az=3D
ed=3D20
> their pieces. But my sculptures were usually just bisqued=3D2C and rarely=
f=3D
ired to=3D20
> cone 1 or 2. Are low fire clays suitable for somewhat large sculptures (f=
=3D
rom=3D20
> bust to torso sized)?=3D20
>=3D20
> Thanks!
=3D
Lee Love on wed 18 aug 10
Rex, it really depends upon what you like working with, and what
effects you want. If you like the colors and textures of high fire,
you can stick with it. If you want the colors of lowfire, you could
explore that. Lowfire can even be used for outdoor sculpture, if you
fire it to lower absorption.
Experiment! See what fits you the best!
--=3D20
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Eric Hansen on wed 18 aug 10
Rex: Lately people have been having a lot of luck with "paper clay" -
you can google that or wait here until Clayarters give you a few links
(which I don't have - hint - )
Also for large sculptures which have interesting ways of shrinking
unevenly - a heavily grogged stoneware works well - I have to ask,
when you say "durable" do you mean for outdoor installation? Salt
fired & wood fired pieces - which are "self-glazing" will last longer
in the outdoor environment, less likely to grow moss, mold, etc. I was
in school with an artist who constructed his pieces in the bed of the
car kiln - up to 4' x 4' x 8' - fire them, and remove with fork lift
truck - these were unglazed but did have engobe paint, first black,
100% coverage, then white on the raised portions, they looked like
large charcoal sketches up to 8 foot & in 3D
I don't see what is wrong with terra cotta for what you do, that is
what it is designed for, right?
h a n s e n
On Wed, Aug 18, 2010 at 1:16 PM, Rex Greg wrote:
> Hi, back in college I did a lot of sculpting with clay. =3DA0I am looking=
t=3D
o get back
> into it, but have a question that I never thought to ask back then.
>
> So, my sculptures are non-utilitarian, and I generally do not glaze them =
=3D
(I
> usually paint them). =3DA0I wanted to know, if I were to fire a piece to =
co=3D
ne 05,
> would a low fire clay whose max firing temp is cone 05 be any stronger/mo=
=3D
re
> durable than a high fire clay (say a cone 10 clay) fired to the same
> temperature (cone 05)? =3DA0Or would the high fire clay be more durable, =
or=3D
would
> they be the same? What about two high fire clays, say cone 6 and cone 10,
> both fired to cone 6? =3DA0Which if any would be stronger/more durable?
>
> I always used high fire clays (cone 10) in college because that's what
> everyone else in the studio used, as many of them were potters who glazed
> their pieces. But my sculptures were usually just bisqued, and rarely fir=
=3D
ed to
> cone 1 or 2. =3DA0Are low fire clays suitable for somewhat large sculptur=
es=3D
(from
> bust to torso sized)?
>
> Thanks!
>
--=3D20
Eric Alan Hansen
Stonehouse Studio Pottery
Alexandria, Virginia
americanpotter.blogspot.com
thesuddenschool.blogspot.com
hansencookbook.blogspot.com
"To me, human life in all its forms, individual and aggregate, is a
perpetual wonder: the flora of the earth and sea is full of beauty and
of mystery which seeks science to understand; the fauna of land and
ocean is not less wonderful; the world which holds them both, and the
great universe that folds it in on everyside, are still more
wonderful, complex, and attractive to the contemplating mind." -
Theodore Parker, minister, transcendentalist, abolitionist (1810-1860)
Snail Scott on wed 18 aug 10
On Aug 18, 2010, at 12:16 PM, Rex Greg wrote:
> ...would a low fire clay whose max firing temp is cone 05 be any
> stronger/more
> durable than a high fire clay (say a cone 10 clay) fired to the same
> temperature (cone 05)?
Yes, definitely!
> ... Are low fire clays suitable for somewhat large sculptures (from
> bust to torso sized)?
Absolutely! It's the coarseness of the body,
not its maturation temperature, that primarily
determines suitability for larger scale work.
-Snail
Ron Roy on wed 18 aug 10
Hi Rex,
I would say normally a high fired clay body fired to 04 would not be
much different than a low fire body - both will chip easily.
A cone 6 clay fired to maturity (about 2% absorbency for stoneware -
0% for porcelain) will be stronger than a cone 10 body fired to cone 6.
You may find exceptions but underfired would be weaker in every case I
can think of.
Let me know if you have some specific questions.
RR
Quoting Rex Greg :
> Hi, back in college I did a lot of sculpting with clay. I am
> looking to get back
> into it, but have a question that I never thought to ask back then.
>
> So, my sculptures are non-utilitarian, and I generally do not glaze them =
(I
> usually paint them). I wanted to know, if I were to fire a piece to cone=
05,
> would a low fire clay whose max firing temp is cone 05 be any stronger/mo=
re
> durable than a high fire clay (say a cone 10 clay) fired to the same
> temperature (cone 05)? Or would the high fire clay be more durable, or w=
ould
> they be the same? What about two high fire clays, say cone 6 and cone 10,
> both fired to cone 6? Which if any would be stronger/more durable?
>
> I always used high fire clays (cone 10) in college because that's what
> everyone else in the studio used, as many of them were potters who glazed
> their pieces. But my sculptures were usually just bisqued, and
> rarely fired to
> cone 1 or 2. Are low fire clays suitable for somewhat large sculptures (=
from
> bust to torso sized)?
>
> Thanks!
>
John Post on wed 18 aug 10
There was an article in a Studio Potter magazine that came out
probably about a decade ago that outlined how the brick industry dealt
with and tested their product to withstand freezing and thawing
outdoors.
Last winter I wanted to make some outdoor garden pieces. I used
Rovin's RO-82, a terra cotta body with grog and single fired it to
cone 1-2. Then I set a few pieces outside for the winter. One right
under an eave so that the runoff from my studio roof would deluge it
all winter, and one on my patio. Both pieces made it through a
Michigan winter unblemished in any way.
John Post
Sterling Heights, Michigan
http://www.johnpost.us
Snail Scott on thu 19 aug 10
In general, any clay fired to maturity will be
stronger than any clay fired much below its
maturity, regardless of the maturation
temperature or type of clay.
-Snail
Lee Love on thu 19 aug 10
On Thu, Aug 19, 2010 at 8:49 AM, Snail Scott wr=
=3D
ote:
> In general, any clay fired to maturity will be
> stronger than any clay fired much below its
> maturity, regardless of the maturation
> temperature or type of clay.
Most "functional" problems with earthenware comes from typically
underfired body. But is also what some of earthenware functional
advantages come from, like in shock resistant cooking ware.
If you fire to cone 1 as Pinnell has reported, you get great
strength in an earthenware body.
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/
=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi
Rex Greg on thu 19 aug 10
Yes, I have used paper clay before, but I'm trying to minimize burnoff si=
=3D
nce=3D20
the kiln is in my basement. I have it vented, but still. Yes, I remembe=
=3D
r when=3D20
I used to reclaim the slurry I'd add a good amount of grog to the potters=
=3D
'=3D20
clay. I mainly used those to minimize shrinkage (which is another reason=
=3D
I=3D20
simply bisqued back then).
Usually I don't make outdoor pieces, but I just want to make the=3D20
pieces "strong" because in my past experince, bisqued pieces still tend t=
=3D
o be=3D20
fragile and to chip, especially the more delicate areas when a large, hea=
=3D
vy=3D20
piece is being moved.=3D20=3D20
Thanks to everyone for the advice. I will try going with a lower tempera=
=3D
ture=3D20
stoneware, cone 5 or 6, and fire it all the way.
Vince Pitelka on thu 19 aug 10
John Post's post regarding firing a terracotta to cone 1-2 is right on the
mark. A previous post said that an outdoor claybody should be vitrified,
and then mentioned Val Cushing's guidelines for outdoor claybodies, and
those two statements contradict each other. An outdoor claybody cannot be
truly vitrified unless it is absolutely zero absorption, which is a rare
thing. A very small amount of porosity, which is characteristic of most
stoneware and porcelain claybodies, still admits some moisture, but the
tightness of the fired claybody will not release the pressure of freezing,
and the piece cracks in a hard freeze. What you want is the mechanical
strength of firing high enough to create a fairly well-developed
glassy-phase, but still enough porosity to release the pressure of freezing
moisture. Soft-fired low-fire ware has the porosity, but not the mechanica=
l
strength. High-fired ware has the mechanical strength, but not the
porosity.
The terracotta architectural ornamentation that has survived at least 100
years all over the upper tier of the Midwest and Northeast was all fired to
low-midrange - cone 1 to cone 4. You have to use the right terracotta
formula for this, because some are loaded with glassy frits to develop a
hard, dense claybody for functional use at cone 04. Such claybodies will
bloat and slump if overfired.
Among the claybodies we use at the Craft Center is our Stephenson
Terracotta, originally formulated by John Stephenson for sculpture,
generally fired to cone-04. It is a great terracotta body for our program,
because it has a significant component of fire clay, and if pieces
accidentally end up in high-fire they bloat and slump, but do not melt and
ruin a lot of other work and kiln furniture. If you want to see the
formula, it is at
i
pes%20-%20Mixer%20Load%20Amounts.htm>. This formula fired to cone-1 or
cone-2 works well for outdoor sculpture, but I have never done the proper
absorption tests with samples fired to those temperatures.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
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